Andy Warden reaches into a cardboard box and pulls out a large spherical object, 16in wide and sealed with plain brown paper. It has a flat, cylindrical base and feels tinny and light to handle. Paint it black and daub the word "bomb" on the side and it would look like something straight out of a vintage Batman movie.

"That's a dummy, there's nothing inside it, obviously we can't use anything like that now," he reassures me, as if concerned I might be about to call the bomb squad. "We couldn't get anything like that into the country any more."

Just to discharge this mother of all fireworks would have required a launch pipe the width of a dustbin and as tall as a man. "It would have gone 1,600ft into the air and burst in a circle of around 350-400ft," he says, matter-of-factly. Now though, it is just a conversation piece when his employer, Fireworks International, exhibits at wedding shows and the like.

In another compact storeroom (regulations mean only a limited selection of fireworks can be kept on the premises), Warden shows me some of the pyrotechnical kit he is allowed to use. "This is the tube for launching a 6in shell, the biggest we can use in the UK today," he says, passing me what looks like a oversized, sawn-off drainpipe. "The ball in there would go 600ft in seven seconds and burst about 150ft across."

I nod blankly; he can see I'm struggling to get my head around these ballistic dimensions. "What you see in Disney, when you see the big round bursts, that's what they are," he adds helpfully.

Such a glorious image contrasts sharply with the more prosaic surroundings of Fireworks International's head offices, hidden behind an unmarked blue metal door on an industrial estate in Castle Donington, outside Derby.

A narrow staircase leads up to a cramped loft office, dominated by a huge whiteboard listing the dozens of displays the firm will have launched into night skies up and down the country by the end of Guy Fawkes weekend.

It is not a habitat to which Warden, about as outdoorsy a person as you could ever meet, looks remotely suited. Happily, because he is the firm's display and training manager, his job keeps him out and about most of the time. "I'm not really an office person, to be honest," he admits, as the kettle boils for tea and he clatters around the gloomy kitchen area looking in vain for a drop of milk.

He has just dashed back to meet me from Fakenham in Norfolk, where he has spent the morning helping set up a customer with his pre-ordered display. "It's mega-busy this year," he says in a tone somehow encapsulating excitement and exhaustion in equal measure, before launching into a breakdown of the logistical problems behind staging 40-odd firework displays over four days.

While it's a relief to hear that Warden will not be setting all of them off himself – that honour will be shared by the band of amateur enthusiasts who take time off from their day jobs to work for Fireworks International over its busiest weekend – he will be busy enough. On Thursday he fired a display at Merrill College, Derby, then last night it was over to Bowdon sports club in Altrincham; tonight he will be at Donington Park (followed by a wedding display), and tomorrow he'll round off the weekend with a show at an army barracks.

This gruelling schedule is interspersed with trips back and forth from the company's main national warehouse – for security reasons, I am not allowed to reveal its whereabouts – to supervise the loading of pre-packed firework displays on to vans. With the company running displays from Aberdeen to Redhill this weekend, it's essential that everything runs smoothly.

It comes as no surprise to learn that this is by far the pyrotechnics expert's busiest time of the year. Warden has no problem taking a couple of weeks off in the middle of August, when most workers find holiday time limited due to high demand. But come 1 September, all leave is cancelled.

"We know the score," he says. After the August bank holiday I'm doing 12 to 14 hours a day, seven days a week. But I know that come 5 November, it's pop-pop-pop-pop, and job done."

Clutching a mug of milkless tea, we decamp to a chilly meeting room crammed, rather bizarrely, with baby buggies belonging to a separate trading area of the business. We flick through some of the glossy display brochures Warden has helped design, filled with page after page of fearsome-looking devices with names ranging from the bombastic (Master of the Universe, 100 Shot Thunder King) to the plain bizarre (Sky Gorillas, Midnight Peacock). These, he explains, are category three fireworks, the largest that can be bought and set off by the public. Category one are for indoor use only, category two the sort that come in smaller selection boxes, and category four for professional use only.

One device, called a 21st Century Barrage ("The size of a small fridge!" exclaims the brochure, and costing an eye-watering £195), looks more like a mobile military installation than something to be letting off in the back garden. While I have no doubt the regulations have been carefully thought through, it's still mildly surprising to me that people can handle such big devices on their own. Teaching people how to do this safely, Warden says, is another key part of his job.

Generally, it is pubs and clubs, or organisations like the scouts, who buy this sort of thing, he says. It'll look professional but they will do it themselves. "We do training days for people who buy these packs, a theory side in the morning and lighting them in the afternoon. We do it in daylight so they can understand what they're doing at night."

Having spent his entire 15-year career at Fireworks International, apart from a brief stint as an army logistics driver after leaving school when he was 17, what Warden doesn't know about fireworks and safety probably isn't worth knowing.

"I got into it by chance really," he recalls. "My dad used to do the firework show at the local nursery and the old boss, who's retired now, rang him to ask whether he knew anyone who wanted a job in the warehouse."

Starting out packing boxes, he progressed to warehouse manager before arriving at his role of display and training manager. Now his duties take him as far as China, where all the company's fireworks are manufactured. "We might say we've got an idea for a new firework, or just have a testing night, sitting out and watching 50 fireworks and marking them out of 10," he says.

When I ask what he thinks of people who try to make their own fireworks, his mood darkens. "No, we stay away from all that," he says firmly. "I've heard about people who will buy a firework and take it to bits, but we do not recommend it. You're dealing with an explosive that's been sealed in cardboard to make it compress and burst in a certain way. Even just opening it, there's a chance of it exploding in your hand, it really is dangerous." Unexploded fireworks, he recommends, should be neutralised by soaking them in water for 24 hours before disposal.

The build-up to a major display can begin up to two months in advance, starting with a site risk assessment followed by discussions with the customer about theme, duration and budget. After a brief has been agreed, the display is designed, with selected explosive shells fused together in the warehouse using delay connectors that guarantee a pause of three seconds between each firework. It is all then boxed up and labelled, ready to be delivered to the site on the day.

Setting up requires surprisingly little time. "For a bigger display, we would try to get there about dinnertime-ish," Warden says. "For a £20,000 display, you could do it in a day, no problem."

And once everything is unpacked and set up, not much can get in the way of a good show – although one obstacle causes more problems than most. "Pouring rain, snow, everything, no problem at all," he says. "But if the wind's going the same way as the crowd, so is the debris. We'd either have to move the crowd, move the fireworks or in the worst case, cancel the display and maybe come back the following day."

For now, though, he is striving for blue touch paper perfection this weekend. Once it's over, I wonder, is the pressure even greater to put on a special show at home where his three- and one-year-old daughters are waiting?

"Oh yeah, they want one all right, they say 'Daddy go bang bang'," he chuckles. He shakes his head and sighs. "Believe me though, you've really had enough of fireworks by that point."

Curriculum vitae

Pay Andy gets a basic rate plus £110 for every display he fires personally, which he estimates amounts to "about 35-45 a year from the Isle of Wight to Peterhead".

Hours Chaotic at this time of year, but normal 9 to 5 at other times. "If I have a display to do at the weekend, I'll have a day off in the week."

Work-life balance "It's hard, and I've got two little ones, so it gets harder! But my partner used to work here so she understands how the business works."

Best thing "It's fun and different. And the rewards of people coming up and thanking you. And getting to go to China, seeing how it is on the other side of the world. That's fascinating."

Worst thing "The hours can get a bit much sometimes, they do take their toll on you. In summer, it can be worse because you have to wait for it to get dark before you can start a display. But it's a minor downside."

Overtime

For lunch, Andy tries to be good and have a baked potato. 'But if all else fails it's chips or something like that.' The thing people always say to Andy 'is to crack a joke about everything going off with a bang'. Andy likes to unwind 'by playing with the kids, some good family time'. Andy is a keen climber and in the summer goes up to the Peak District with his brother. 'I used to be a sailing instructor as well, but I've knocked that on the head since the kids came along.' Andy's favourite film is 'either the Shawshank Redemption or the Rock'.